<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>修改属性</title>
    <style>
        div {
            width: 200px;
            height: 200px;
            background-color: black;
        }
    </style>


</head>

<body>
    <div>

    </div>
    <script>
        // 修改style样式操作，产生的是行内样式，css权重比较高
        var div = document.querySelector('div')
        div.onclick = function () {
            div.style.backgroundColor = '#77ff'
            this.style.width = '500px'
        }
    </script>
</body>

</html>